Satellite direct radio broadcast system

ABSTRACT

A satellite direct audio broadcast system includes a plurality of fixed-rate, uniform, frequency division multiple access (“FDMA”) uplinks and a time division multiplexed (“TDM”) downlink. Source audio channels may be divided among and transmitted through a selectable number of fixed-rate uplinks so as to have selectable audio quality at the receiver. Fixed-rate FDMA uplinks include information designating related channels as containing related source information. On-board the satellite baseband processing selects uplink information channels for inclusion into none, one or multiple TDM downlinks. Transmitted audio information may be scrambled, and authorization downloaded to receivers to permit descrambling for paid subscription service.

This application is a continuation of application Ser. No. 09/124,997,filed Jul. 30, 1998, now U.S. Pat. No. 6,249,514 which is a continuationof application Ser. No. 08,569,346, filed Dec. 8, 1995, now issued asU.S. Pat. No. 5,835,487.

BACKGROUND OF THE INVENTION

The invention relates to the field of satellite direct radio broadcast,and in particular to a satellite-based broadcast communication systememploying frequency division multiplex uplinks and time divisionmultiplex downlinks and for broadcasting and audio (voice and music)programming.

Early satellite communication systems used space-based radio frequencytransponders which acted as simple repeaters. In one typical scheme,multiple sources each transmit at a separate uplink carrier centerfrequency (uplink FDMA), and the satellite transponder repeated eachsignal at a separate downlink carrier frequency (downlink FDMA). Inanother typical scheme, multiple sources each transmit bursts at thesame carrier frequency in a coordinated fashion so that bursts fromdifferent transmitters do not collide (TDMA), and the transponderrepeated all signals in a single downlink carrier. Still other schemesutilize multiple antenna beams and on-board-the-satellite switching sothat signals in one uplink beam could be controllably switched to aselected downlink beam.

Many prior systems require substantial transmit and/or receiveequipment. Furthermore, despite the various types of systemarchitectures, there has not been implemented a system suitable fordirect broadcast of audio radio programming to low-cost consumer radioreceivers.

SUMMARY OF THE INVENTION

There presently exists a population of over 4 billion people that aregenerally dissatisfied and undeserved by the poor sound quality ofshort-wave radio or the coverage limitations of amplitude modulation(“AM”) band and frequency modulation (“FM”) band terrestrial radiobroadcast system. This population is primarily located in Africa,Central and South America, and Asia. The satellite Direct AudioBroadcast (“DAB”) system of the present invention is intended to providehigh quality radio channels accessible to people worldwide who currentlyreceive, with various kinds of limitations, terrestrial radioprogramming.

An object of the present invention is to provide a satellite directradio audio broadcast system suitable for transmitting audio signals,such as voice and music programming, to low-cost consumer radioreceivers.

A further object of the present invention is to provide a satellitedirect audio broadcast system suitable for transmitting multiple audiosignals from a variety of sources and signal qualities, such as “AM”band quality monaural, “FM” band quality stereo, and “CD” quality stereoto low-cost consumer radio receivers.

A further object of the present invention is to provide a satellitedirect audio broadcast system capable of providing individual uplinkbroadcasters with direct access to the satellite, yet also capable ofpreventing unauthorized broadcasts from being received by consumerradios.

A further object of the invention is to provide a satellite direct audiobroadcast system capable of providing subscription (paid reception)service by low-cost consumer radio receivers yet also capable oflimiting service to non-subscription receivers in the same service area.

These and other objects of the invention are achieved by providing asatellite direct audio broadcasting system having frequency divisionmultiple access uplinks (FDMA) and time division multiplexed (TDM)downlinks. Broadcast stations transmit one or more “prime rate”channels, each having a source signal data rate of sixteen (16)kilobit-per-second (kbps) data rates. Each prime rate channel istransmitted on a separate carrier. At the satellite, prime rate uplinkchannels are multiplexed into a single TDM channel. Radio receiversdemultiplex the TDM downlink and recombine one or more prime ratechannels to provide the selected quality of service. A system controlcenter provides centralized command over the satellite.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to attached drawings inwhich:

FIG. 1 illustrates the principle of operation of the processedcommunication mission in a satellite system of the present invention;

FIG. 2 illustrates a re-allocation of information from uplink frequencydivision multiple access channels into a downlink time divisionmultiplexed channel in a satellite communication system of the presentinvention;

FIG. 3 illustrates satellite signal processing in a satellitecommunication system of the present invention;

FIG. 4 illustrates a satellite processor in a satellite communicationsystem of the present invention;

FIG. 5 illustrates a transparent satellite transponder arrangement in asatellite communication system of the present invention;

FIG. 6 illustrates program signal processing in a satellitecommunication system of the present invention;

FIG. 7 illustrates program signal processing in a portable radioreceiver in a satellite communication system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS System Overview

The system preferably will consist of three geostationary satellites,low cost radio receivers, and associated ground control networks. Thepreferred satellites cover the African-Arabian region, Asian region andthe Caribbean and Latin American regions from the followinggeostationary orbits:

-   21° E orbital location, providing DAB to Africa and Middle East-   95° W orbital location, providing DAB to Central and South America-   105° W orbital location, providing DAB to South-East Asia, and    Pacific rim

The preferred system uses the frequency band of 1467 to 1492 MHz, whichhas been allocated for Broadcasting Satellite Service (BSS) DAB at WARC92, that is, in accordance with resolutions 33 and 528 of the ITU. Thebroadcasters use feeder uplinks in X band, from 7050 to 7075 MHz.

The system will use digital audio coding techniques. Each satellite willdeliver digital radio audio signals having qualities equivalent to AMmonaural, FM monaural, FM stereo and CD stereo throughout its respectivecoverage area, together with ancillary data such as paging, video imagesand text transmissions directly to the radios. The system may alsodeliver multimedia services such as large database downloads to PCs forbusiness applications, map and printed text information for travelers,and even color images to augment audio programs for advertising andentertainment.

Each satellite preferably will be equipped with three downlink spotbeams, having beam widths of about 6°. Each beam covers approximately 14million square kilometers within power distribution contours that are 4dB down from beam center and 28 million square kilometers withincontours that are 8 dB down. The beam center margin may be 14 dB basedon a receiver gain-to-temperature ratio of −13 dB/K.

FIG. 1 illustrates the principle of operation of a satellite system ofthe present invention. The uplink signals 21 issue from broadcasters viaindividual frequency division multiple access (“FDMA”) channels fromearth stations 23 located anywhere within the terrestrial visibility ofthe satellite with elevation angles higher than 10°. Each broadcasterhas the ability to uplink directly from its own facilities to one of thesatellites placing one or more 16 kbps prime rate channels on a singlecarrier. Alternately, broadcasters which have no capacity for directaccess to the satellite may have access through a hub station. Use ofFDMA for uplink offers the highest possible flexibility between multipleindependent broadcast stations.

Conversion between uplink FDMA and downlink MCPC/TDM is achieved onboard the satellite at the baseband level. At the satellite 25, eachprime rate channel transmitted by a broadcast station is demultiplexedinto individual 16 kbps baseband signals. Individual channels are routedto one or more of the downlink beams 27, each of which is a single TDMsignal. This baseband processing provides a high level of channelcontrol in terms of uplink frequency allocation and channel routingbetween uplink and downlink. Uplink signals are received in thesatellite in X band and down converted to L band.

Downlinks use multiple channel per carrier time division multiplexing.One of these carriers is used in each of the three beams on eachsatellite. TDM quadature phase shift key (“QPSK”) transmission isperformed using concatenated Forward Error Correction (FEC) coding, andSystem A (COFDM) using a Viterbi FEC coding.

FIG. 2 illustrates the re-allocation of prime rate channels from uplinkfrequency division multiple access channels into a downlink timedivision multiplexed channel in a satellite communication system of thepresent invention. The overall uplink capacity is preferably betweentwo-hundred-eighty-eight (288) and three hundred eighty four prime rateuplink channels 31 of sixteen (16) kbps each. Ninety six (96) prime ratechannels 33 are selected and multiplexed for transmission in eachdownlink beam 35 time division multiplexed onto a carrier ofapproximately 2.5 MHz bandwidth. Each uplink channel may be routed toall, some or none of the downlink beams. The order and placement ofprime rate channels in a downlink beam is fully selectable from atelemetry, range and control (“TRC”) facility 24.

The carrier frequencies in each downlink beam are different to enhancebeam-to-beam isolation. Each TDM downlink channel is operated in thesatellite payload at saturation, giving the highest possible powerefficiency in terms of link performance. Use of single carrier pertransponder operation achieves the most efficient operation of thesatellite communication payload in terms of conversion of solar powerinto radio frequency power. This is far more efficient than techniquesrequiring simultaneous amplification of a multiplicity of FDM carriers.The system produces high receive margins suitable for stationary andmobile reception indoors and outdoors.

Radio Channel Capacity

The system incorporates source coding using MPEG 2, Layer 3 whichachieves the cited qualities at bit rates of 16, 32, 64 and 128 kbpsrespectively. Error rates over the system will be less than 10⁻¹⁰ andthus are also suitable for high quality digital image and datatransmission for multimedia services. The MPEG 2 layer III coding offersa better bit rate efficiency than the previous MPEG 1 layer II (Musicam)standard for the same audio quality. The digitally coded source bitrates are:

-   16 kbps for monophonic voice,-   32 kbps for monophonic music, with near FM quality,-   64 kbps for stereophonic music, with near FM quality,-   128 kbps for stereophonic music, with near CD quality.

Gain on bit rates are about 50%, depending on the quality, with respectto layer II. The MPEG 2 layer III coding is downward compatible andallows, for example, the use of MPEG 1 layer II if needed.

In the preferred implementation, each satellite has the capacity totransmit a total capacity of 3072 kbps per beam which may be anycombination of the above audio services. This corresponds to a capacityper beam of:

-   192 monophonic voice channels, or-   96 monophonic music channels, or-   48 stereophonic music channels, or-   24 CD stereophonic music channels, or any combination of the above    signal quality.

The overall system will deliver the digital signals with a bit errorrate (BER) of 10⁻⁴ or better, providing the various service qualitiespreviously defined. For each downlink TDM in L band issued from thesatellites, the Edge Of Coverage EIRP of the TDM carrier will be 49.5dBW. This EIRP, together with specific Forward Error Correction, insuresa minimum 9 dB margin for a 10⁻⁴ BER, using the baseline radio receiverantenna. This margin will help combat signal loss due to obstacles inthe path between the satellite and the receiver, providing full qualityreception in the intended coverage area.

Radio receivers in disadvantaged locations can be connected to a largegain antenna, or to an antenna located in an unobstructed position. Forexample, reception in large buildings may need a common roof antenna forthe entire building or individual reception antennas near a window. Atthe 4 dB down contour of the earth coverages, the channels have anestimated margin of 10 dB relative to the power density needed todeliver a bit error rate of 10⁻⁴. At beam center this margin estimate is14 dB.

Prime rate channels are the building blocks of the system and can becombined to achieve higher bit rates. Prime rate channels can becombined to create program channels at bit rates up to 128 kilobits persecond. The operating margin does not change for the higher bit rates.Within the 4 dB contour, most radios will view the satellite atelevation angles of greater than 600 making interference from structuresvirtually nil. Within the 8 dB contour the elevation angle to thesatellite will be greater than 50° which may experience occasionalinterference due to reflections or blockage from structures.

The Satellite

The system includes a baseband processing satellite payload. Basebandprocessing allows improved system performance, at least for uplink anddownlink link budgets, management of broadcast stations, and control ofthe downlink signals.

FIG. 3 illustrates satellite signal processing in a satellitecommunication system of the present invention. The coded prime rateuplink carriers are received at an X-band receiver 41. A polyphasedemultiplexer and demodulator 43 receives the 288 individual FDMAsignals, generates a single analog signal on which the data of the 288signals is time multiplexed, and performs a high-speed demodulation ofthe serial data. A routing switch and modulator 45 selectively directsindividual channels of the serial data into all, some or none of threedownlink signals, and further modulates and upconverts the threedownlink signals. Traveling wave tube amplifiers 47 boost the threedownlink signals, which are radiated to earth by L-band transmitantennas 49. The satellite also includes a demultiplexer 42 andamplifier group 44, which is configured in a conventional “bent pipe”signal path which frequency converts input signals for retransmission.

FIG. 4 illustrates a satellite baseband processor 51 and associateddownconverter 53 and upconverter 52 elements in a satellitecommunication system of the present invention. The downconverterreceives 288 carriers in a wideband input to a divider 61. The dividerprovides eight, six-hundred megahertz output ports each capable ofcarrying forty-eight (48) of the uplink prime rate channels (stillmodulated on separate carriers). A first, eight-for-six redundantdownconverter 63 (operating in conjunction with synthesizer 64)selectively drops any selected input to an intermediate frequency ofabout one hundred and forty megahertz. Although eight redundantdownconvert paths are provided, only six are required for thetwo-hundred and eighty-eight prime rate channels.

A second, eight-for-six redundant downconverter 65 (operating inconjunction with local oscillator 66) drops selected intermediatefrequency inputs to a baseband signal of about three megahertz. As withthe first downconverter, eight paths are provided while only six arerequired.

The baseband processor 51 includes eight redundant chains of analog todigital converters 54 and demodulators 55. Each A/D converter receives asingle signal having forty-eight prime rate channels still on separatecarriers. The demodulator includes a polyphase demultiplexer/demodulatorthat produces a single output with information from the prime ratechannels time multiplexed. Router 56 includes digital memory storagesuch that the serial data streams from all selected demodulator chainsare stored as received, and which allows data for each of thetwo-hundred eighty eight channels to be read out to any of fiveredundant output paths. Three paths are active at a time (one for eachdownlink beam), and the additional paths are provided for redundancy.Each output path will receive data in parallel for ninety six prime ratechannels. Any prime rate channel may be read out to none, some or allselected output paths. Cross matrix elements 57 serve to time divisionmultiplex data from the ninety-six selected prime rate channels into asingle TDM digital signal. Modulators 58 and digital to analogconverters 59 generate quadrature-phase-shift-key modulated basebandsignals with about a three megahertz bandwidth. A first, five-for-threeredundant upconverter 67 (in conjunction with local oscillator 68)modulates selected baseband signals to an intermediate frequency ofabout one-hundred and forty megahertz. A second, five-for-threeredundant upconverter 69 (in conjunction with synthesizer 70) upconvertselected intermediate-frequency signals to L-band (near fifteen hundredmegahertz).

Each carrier is amplified to a power of 300 watts by an amplifierconsisting of multiple, parallel connected traveling wave tubes. Becauseonly one carrier is amplified by each tube, it is possible to operatethe tubes near their maximum saturated power output. Suchsingle-carrier-per-tube operation permits far more efficient use of theonboard spacecraft power resources than can be achieved by moreconventional multiple FDMA carrier operation. An advantage of 3 to 4 dBin terms of more power available to the downlink channels results. Thebandwidth required to accommodate each carrier is 2.5 MHz. Carriers canbe located on frequency centers separated by 500 kHz spacings anywherein the band. Carrier separations on the same satellite must be at least2.5 MHz.

Each satellite will also be equipped with a transparent transponderarrangement as shown in FIG. 5. A divider 71 separates the widebanduplink into five paths each having a bandwidth of about six-hundredmegahertz. A five-for-three redundant downconverter 73 (in conjunctionwith synthesizer 74) drops the radio frequency signal of the selectedpath to an intermediate frequency of about one-hundred forty megahertz.Five-for-three redundant surface acoustic wave (SAW) filters 75 removeuplink noise. A five-for-three upconverter 77 (in conjunction withsynthesizer 76) translates the filtered intermediate frequency signalsto L-band around fifteen hundred megahertz. This arrangement repeats anadditional 96 prime rate channels on a downlink MCPC time divisionmultiplexed carrier that is formatted at an uplink hub broadcaststation. One such station could serve all three beams or different hubscould be used for each beam. Each repeated MCPC time divisionmultiplexed carrier will have the same downlink waveform, the samepower, but the opposite polarization and/or different carrier frequencyas the one generated onboard the satellite. Thus, the total capacity perbeam will be 192 prime rate channels.

High redundancy in the spacecraft receivers, digital processors andoutput high power amplifiers guarantees a 12 year life for eachsatellite. Also there is enough position keeping fuel to maintain eachsatellite to a location within ±0.10° of its assigned orbit position for15 years.

The time division multiplex frames have a duration of 1 second, eachmarked by a 40 symbol synchronization word. The downlink multiplechannel per carrier (MCPC) time division multiplexed carrier has a rateof 1.767688 million QPSK symbols per second.

The satellites are operated by a ground control segment and managedaccording to traffic requirements by a mission control segment duringthe orbit lifetime. The bit rates and consequently qualities can bemixed in any beam to meet the demand for service. The bit-rate/qualitycomplexion of the service can be easily changed from ground command andcan vary at different times of the day. In the preferred embodiment,channel allocation may be changed on an hour-by-hour basis according toa program schedule established twenty-four hours in advance. Radioreceivers, relying on ensemble information included in each prime ratechannel, will automatically select those prime rate channels necessaryto generate the user-selected audio program.

Uplink Broadcast Stations

FIG. 6 illustrates program signal processing in a satellitecommunication system of the present invention. Two sources are shown inFIG. 6, and it should be understood that additional channels may beadded with similar signal processing. Signal sources 101 are firstsubject to MPEG 2 layer III coding 103. The source coded digital signalsfor the various program channels are forward-error-correction codedusing a concatenated channel coding scheme comprising a 255,223 ReedSolomon block coder. The block coder 105 is followed by a blockinterleaver 107, and then by a rate 1/2 Viterbi convolution coder 109.

Use of such a concatenated coding scheme contributes to the low biterror rate achieved over the system. Channel coding multiplies the bitrate needed for transmission by a factor of 2×255/223. Thus, the primerate is increased to 36.72 kilobits per second after coding.

Depending on the program channel rate, the coded program channels arenext split among a set of coded prime rate transmit channels. Additionof the control word and preamble code raises the transmitted primechannel rate to 36.826 kilobits per second.

For example, a 128 kbps channel is split into eight channels as follows:

Symbol 1 into physical channel 1

Symbol 2 into physical channel 2

Symbol 3 into physical channel 3

Symbol 4 into physical channel 4

Symbol 5 into physical channel 5

Symbol 6 into physical channel 6

Symbol 7 into physical channel 7

Symbol 8 into physical channel 8

Symbol 9 into physical channel 1 etc.

A control word 111 in each coded prime rate channel identifies thedigital group to which it belongs and carries instructions that allowthe receiver to recombine the coded prime rate channels to reconstructthe coded program channels. An exemplary eighty (80) bit control wordis:

# Bits Indication 2 Quantity of related ensembles (00 = no relation,four related ensembles maximum) 2 Ensemble Identification Number (00 =Ensemble #1, 11 = Ensemble 4) 4 Ensemble type (0000 = Audio, 0001 =Video, 0010 = Data, other types or reserved) 3 Quantity of 16 kbps primerate channels in ensemble (000 = 1 channel, 001 = 2 channels, . . ., 111= 8 channels) 3 Prime Rate Channel Identification Number (000 = channel1, . . ., 111 = channel 8) 3 Quantity of sub-ensembles (000 = 1, . . .,111 = 8) 3 Quantity of 16 kbps prime rate channels in sub-ensemble (000= 1, 111 = 8) 2 Sub-Ensemble Identification Number (000 = Ensemble #1, .. ., 111 = Ensemble 8) 3 Ensemble/Sub-Ensemble blocking (000 = noblocking, 001 = type 1 blocking, . . ., 111 = type 7 blocking) 11reserved 40 CRC.

The control word entry for the Quantity of Related Ensembles allows arelationship to be created between various groups of ensembles. Forexample, a broadcaster may wish to provide related audio, video and dataservices, such as electronic newspaper with audio text, and additionalinformation. The Ensemble Identification Number identifies the ensemblenumber of which the channel is a part. The Quantity of 16 kbps primerate channels in ensemble defines the number of prime rate channels inthe ensemble. The Quantity of SUB-ENSEMBLES and QUANTITY of 16 KBPSprime rate channels in sub-ensemble defines a relationship within anensemble, such as, in a CD quality stereo ensemble, use of four primerate channels for a “Left Stereo” signal and four different prime ratechannels for a “Right Stereo” signal. Alternately, music may beassociated with multiple voice signals for announcers, each voice signalin a different language. The Quantity of 16 kbps prime rate channels insub-ensemble defines the number of prime rate channels in thesub-ensemble. The Sub-Ensemble Identification Number identifies thesub-ensemble of which the channel is a part.

The Ensemble/Sub-Ensemble blocking bits allow cooperative blocking ofbroadcast information. For instance, some countries may prohibitadvertising for alcohol. Radios produced for that country can be presetwith a code, or a code can otherwise be loaded, so that the radio wouldrespond to the blocking signal and block the specific information.

Each prime rate channel will be organized into frames having at least achannel preamble to provide a timing reference between the broadcaststation and the satelite. The preamble may include a unique word toidentify the start of the block coding for each frame. The preamble mayalso include a block of timing bits containing 12–14 bits. When thebroadcast station and the satellite are synchronized, the block contains13 bits. If, due to differences in oscillators in the satellite andbroadcast station, the broadcast station lags behind or moves ahead byone bit, the block of timing bits is shortened or lengthenedaccordingly. All channels may use the same preamble. When a source hasbeen split among multiple prime rate channels, the preambles for allrelated channels should be coincident. There is no master clocksynchronization between separate broadcast stations. Addition of thecontrol word and preamble code raises the transmitted prime channel rateto 36.826 kilobits per second.

Each coded program source is divided into individual prime ratechannels. In the example shown, program source 1 comprises four primerate channels, which represents an FM quality stereo signal. Programsource 2 comprises six prime rate channels, which can be used as a “nearCD” quality stereo signal, or an FM quality stereo signal linked to a 32bit data channel (e.g., for transmitting an image signal for display ona radio receiver liquid crystal display (“LCD display”)). Alternately,the six prime rate channels can be used as a 96 kbps broadcast datachannel. Each prime rate channel is modulated by a separate QPSKmodulator 117 to an intermediate frequency. Upconverter 119 moves theseparate prime rate channels to the FDMA uplink band, and theup-converted channels are transmitted through amplifier 121 and antenna123. Broadcast uplink stations use VSAT signals for transmission ofelementary (16 kbps) channels, using small antennas (2 to 3 metersdiameter).

The prime rate uplink channels are transmitted to the satellite onindividual Frequency Division Multiple Access (FDMA) carriers. Up to 288uplink prime rate carriers can be transmitted to the satellite in itsglobal uplink beam. Small broadcasters' earth terminals equipped with2.4 m diameter parabolic X-band antennas and 25 watt power amplifierscan easily transmit a 128 kilobit per second program channel (comprising8 of the prime rate channels) to the satellite from a site in thecountry originating the program. Alternatively, program channels can beconnected to shared uplink earth terminals via leased PSTN terrestriallinks. The system has adequate uplink capacity for every country in itsworld coverage to have its own satellite radio broadcasting channel.

Radio Receivers

The radio receiver is intended to provide maximum convenience of use ata minimum cost. Low end, rudimentary radios are expected to cost theconsumer approximately U.S. $50 based on mass-produced ASIC chips, andcapable of operating with solar power or batteries. The radio willreceive the L band signal, demodulate and extract from the TDM streamthe useful audio signal, and expand the sound into its original form.

FIG. 7 illustrates program signal processing in a portable radioreceiver in a satellite communication system of the present invention.Such a low cost radio receiver, equipped with a small compact patchantenna 131 having about 4 to 6 dBi gain, will require virtually nopointing and will tune automatically to selected channels. Analternative higher end radio will be equipped with an antenna thatachieves 10 to 12 dBi of gain. Since such an antenna would be quitedirectional, it is pointed to achieve best reception. One version ofthis antenna may be an array of patches. The array may be embeddedconformally into the surface of the radio case, attached as a lid or becompletely detachable and connected to the radio by a thin coax cable afew meters long. Another version of the antenna could be a helixoperating in either a broadside or end-fire mode. Pointing is done byrotating the antenna in elevation and azimuth. A detachable antennamight be mounted on a small tripod on the ground or mounted to a windowframe and pointed to achieve best reception. A 10 dBi antenna has a beamwidth of approximately 650 and consequently will be easy to point at thesatellite for achieving optimum reception. The directivity of thisantenna will further enhance reception in locations where reflectionsmight otherwise cause interference. A phased array, rod shaped antennawith wide beamwidth in one dimension but narrow in the other (i.e. a fanbeam) is another alternative. Yet an alternate antenna could be a spiralantenna for outdoor reception and most indoor reception. In certainenvironments (mask, concrete or metal buildings), indoor reception mayrequire connection to an external antenna. For reception by mobiles,antennas with as little as 4 dBi of gain may be mounted on the vehicle.A single antenna of this type would operate very well in an openlocation at high elevation angles, devoid of severe multipathreflectors. However in an area having multipath reflections, such asdowntown cities, where elevations are less than 60°, measures mayoccasionally have to be taken to mitigate the multipath interference.One such measure is to use two or three of the 4 dBi gain antennas in aspatial diversity array mounted at various locations on the vehicle.These would be dynamically added to achieve directivity or combined soas to pick the maximum signal arrival at a given instant. Anotheralternative is to install a steerable fan beam directional antenna with10 dBi of gain and make it track the satellite. This latter idea isexpensive but people of means may well prefer its use to maximallybenefit from the high performance quality offered by the system. Assatellite mobile systems come into worldwide use in the next decade,electronically steerable array antennas are expected to drop in priceand become generally affordable.

A time division multiplexing, multiple channel per carrier technique isused for downlink transmission to the radios. Each of the prime rate(16.056 kilobits per second) channels occupies its own time slot in thetime division stream. These prime rate channels are combined to carryprogram channels ranging from 16 to 128 kilobits per second. Use ofdigital techniques allows for ancillary services to the radio includingslow motion image, paging, mailing, fax, use of flat screens or serialinterface. This data and information may be multiplexed within the audiodigital signal channels.

Each radio receiver can tune to one of the 1.767688 million symbol persecond TDM carriers transmitted in one of the beam coverages. As shownin FIG. 7, a low noise amplifier 133 boosts the satellite signal, andthe boosted signal is received in a chip set 135. The chip set 135includes a receiver 137, demodulator 139, time division demultiplexer141 (which recovers the prime rate channels) and forward errorcorrection (“FEC”) decoder 143. The output of the chip set 135 is abaseband digital signal.

The instructions needed for the receiver to control recombination of thecoded prime channels into the coded program channels are contained inthe control word imbedded in each coded prime rate channel. Therecombined coded program channels thus recovered are decoded anddeinterleaved to recover the original baseband prime rate bit streamthat entered the system at the broadcaster's earth terminal. Therecovered bit streams are next converted back to the analog audio signalby a source decoder 145. The system can reproduce various audioqualities ranging from AM monaural to CD stereo depending on the programchannel bit rate.

The user will control the whole functionality with five knobs. Allinformation will appear on an LCD with 80 characters. For all systemcontrol functions, a micro controller with integrated LCD driver will beused. The integrated LCD driver allows the use of cheap LCD without anyadditional logic and reduces the number of parts needed. Themicrocontroller should provide 16 kbyte ROM, 512 kbyte RAM.

Subscription Service

The system may incorporate subscription service under which certainprogram channels may be received only after a subscriber (radio receiverowner/user) has paid for service. The broadcaster of the subscriptionchannel scrambles the broadcast. Unpaid receivers would receive anoise-like signal. A paid subscriber would then have his/her radioauthorized to descramble the subscription channel. Such descrambling canbe accomplished by a decryption key.

Authorization can be accomplished in one of several ways. In a firstmethod, the paid subscriber inserts a smartcard or memory cardcontaining authorization to descramble the selected channel. Thesmartcard could also be equipped with a digital payment program thataccounts for time and usage, or a debit card that is initialized with apayment amount and decrements as the receiver is used. (When the paymentdecrements to zero, the subscriber must pay for additionalauthorization.) In a second method, the paid subscriber could deliverhis/her receiver to an authorized agent who downloads the requiredauthorization through a digital data port on the receiver. In a thirdmethod, each radio receiver would have a unique, embedded identificationnumber, and the broadcaster could include a one-bit-per-frame controlchannel within the broadcast preamble. When a subscriber pays for theservice, the broadcast channel addresses the radio and provides anauthorization signal. By whatever method, a specially designed microchipwould be preferred to control authorization, either in the smart card orin the receiver itself.

After learning of the embodiments described above, people practicing inthis art will be able to make variations that fall within the spirit andscope of the invention. The embodiments described above are exemplarybut not intended to limit unduly the scope of the invention as definedby the following claims.

1. A communication system comprising: a plurality of frequency divisionuplinks, each uplink comprising an information channel; a space segmentreceiving the uplinks, restoring data from the information channels inthe uplinks to baseband data, and combining data from selectedinformation channels into at least one time division multiplex signal;at least one time division multiplex downlink comprising said at leastone time division multiplex signal; and a broadcast station fortransmitting a source signal divided among selected ones of theplurality of frequency division uplinks, each of the selected uplinkscomprising information designating the selected uplinks as related toeach other.
 2. The communication system of claim 1 including a pluralityof uniform-rate uplinks.
 3. The communication system of claim 1 whereinthe uplinks each comprise at least one uniform rate channel and an audiosource program is divided among a plurality of uniform rate channels. 4.The communication system of claim 3 wherein the audio source program ischaracterized by one of a plurality of qualities of service forbroadcasting the audio signal comprising amplitude modulated monauralsignal quality, frequency modulated monaural signal quality, frequencymodulated stereo signal quality, and optical disc stereo signal quality.5. The communication system of claim 1 further including a radioreceiving a time division multiplexed downlink and generating an outputfrom a selectable plurality of uniform rate information channels.
 6. Thecommunication system of claim 1 wherein the broadcast station transmitsan audio signal as a plurality of related frequency division uplinks,each uplink including information designating the uplinks as related. 7.The communication system of claim 1 wherein the broadcast stationtransmits scrambled audio signals as a plurality of related frequencydivision uplinks, each uplink including information designating theuplinks as related.
 8. The system of claim 1 further including asatellite control station that commands the space segment to reconfigurerouting of selected uplink information channels into the downlink. 9.The system of claim 1 further including a satellite control station thatcommands the space segment to reconfigure routing of selected uplinkinformation channels into a plurality of downlinks.
 10. Thecommunication system of claim 1 further comprising a plurality of timedivision multiplex downlinks.
 11. The communication system of claim 10further comprising a satellite control station that commands the spacesegment to route selected uplink information channels into selected onesof the plurality of time division multiplex downlinks.
 12. Thecommunication system of claim 1 wherein the information channelcomprises data selected from the group consisting of paging signals,video, graphic images, database data, file transfer data, maps and text.13. A communication system for the broadcast and reception of programscomprising: a plurality of frequency division multiplex uplinks, eachuplink including at least one information channel, the programsconsisting of a variable number of uniform rate channels that are eachcharacterized by a minimum signal rate, the information channel in eachuplink comprising at least one uniform rate channel corresponding to arespective one of the programs, each uniform rate channel having acorresponding control word, the system being programmable to combineuniform rate channels corresponding to at least one program and locatedin different information channels into a digital signal group having ahigher signal rate than the minimum signal rate and to provide thecontrol word in each uniform rate channel in the digital signal groupwith at least one bit to indicate that the uniform rate channel belongsto the digital signal group; a space segment receiving the uplinks,restoring data from the information channels to baseband data, andcombining the baseband data from selected information channels into atleast one time division multiplexed signal; and at least one timedivision multiplex downlink including the time division multiplexedsignal.
 14. A method of broadcasting a program to at least one receivervia a space segment comprising the steps of: formatting a program into aplurality of uniform rate channels, each uniform rate channel having acorresponding control word indicating that the uniform rate channel isrelated to another uniform rate channel; modulating the uniform ratechannels onto different ones of a plurality of frequency divisionuplinks; processing the uplinks via the space segment to recover theuniform rate channels as baseband data; and routing the baseband datainto selected time slots in at least one time division multiplexdownlink signal.
 15. The method of claim 14 wherein the routing stepcomprises the step of routing the baseband data into selected time slotsin selected ones of a plurality of time division multiplex downlinksignals.
 16. The method of claim 15 further comprising the step ofgenerating control signals to dynamically control routing of basebanddata into one of the downlink signals by the space segment.
 17. Themethod of claim 14 wherein the formatting step comprises the step ofcombining an audio program with ancillary data selected from the groupconsisting of paging signals, video, graphic images, database data, filetransfer data, maps and text into a number of related uniform ratechannels.
 18. A method of formatting programs for broadcast to at leastone receiver via a space segment comprising the steps of: dividing eachof the programs into a number of uniform rate channels, each uniformrate channel being characterized by a minimum signal rate; providingeach uniform rate channel with a control word; combining the uniformrate channels corresponding to at least one program into a digitalsignal group having a higher signal rate than the minimum signal rate;and providing the control word in each uniform rate channel in thedigital signal group with at least one bit to indicate that the uniformrate channel belongs to the digital signal group.
 19. A method asclaimed in claim 18, further comprising the step of providing data ineach control word, the data being selected from the group consisting ofbits representing a number of related digital signal groups, bitsuniquely identifying the digital signal group to which a uniform ratechannel associated with the control word belongs, bits representing thenumber of the uniform rate channels in the corresponding digital signalgroup, bits uniquely identifying the uniform rate channel correspondingto at control word, bits representing a number of sub-ensemble,constituting at least one digital signal group, bits representing thenumber of uniform rate channels in a sub-ensemble, and bits uniquelyidentifying a sub-ensemble.
 20. A method as claimed in claim 18, furthercomprising the step of providing data in each control word to indicatewhich of audio, video and data constitute the corresponding uniform ratechannel.
 21. A method as claimed in claim 18, further comprising thestep of providing blocking bits in the control word of selected uniformrate channels to prevent reception of at least a portion of the selecteduniform rate channels by the receiver.
 22. A broadcast communicationsystem comprising: a plurality of frequency division multiplexeduplinks, each of said uplinks comprising an information channel; a spacesegment for receiving said uplinks, restoring data from said informationchannels to baseband data, and combining said data from selected ones ofsaid information channels into at least one time division multiplexedsignal; and at least one time division multiplexed downlink comprisingsaid at least one time division multiplexed signal; wherein each of saiduplinks has a uniform rate and is provided with a control wordindicating that said information channel in each of said uplinks isrelated to at least another said information channel, said uplinkscorresponding to uniform-rate uplink channels, and a source program tobe broadcast via, said broadcast communication system is divided among aplurality of said uniform-rate uplink channels.
 23. A broadcastcommunication system comprising: a plurality of frequency divisionmultiplexed uplinks, each of said uplinks comprising an informationchannel; a space segment for receiving said uplinks, restoring data fromsaid information channels to baseband data, and combining said data fromselected ones of said information channels into at least one timedivision multiplexed signal; at least one time division multiplexeddownlink comprising a time division multiplexed signal; and a broadcaststation configured to process a program signal for broadcast via saidspace segment by scrambling said program signal, dividing said programsignal among a plurality of selected ones of said uplinks, and providingcontrol data in each of said selected ones of said uplinks to indicatethat said selected ones of said uplinks are related.
 24. A broadcastcommunication system comprising: a plurality of frequency divisionmultiplexed uplinks, each of said uplinks comprising an informationchannel; a space segment for receiving said uplinks, restoring data fromsaid information channels to baseband data, and combining said data fromselected ones of said information channels into at least one timedivision multiplexed signal; at least one time division multiplexeddownlink comprising said at least one time division multiplexed signal;and a radio for receiving said downlink; wherein the information channelof a number of said uplinks is provided in said time divisionmultiplexed signal via said space segment, said radio being configuredto generate an output from said information channel of selected ones ofsaid uplinks provided in said downlink, said information channel of saidselected ones of said uplinks designating said selected ones of saidunlinks as related to each other.
 25. A broadcast communication systemas claimed in claim 24, further comprising a satellite control stationconfigured to command said space segment to route said informationchannel of selected ones of said uplinks into said downlink.
 26. Abroadcast communication system as claimed in claim 24, furthercomprising a second downlink, said satellite control station configuredto command said space segment to route said information channel ofselected ones of said uplinks into one of said downlink and said seconddownlink.